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jetting slant fcr 39 MRD/ SSW help


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Hi all , I was hoping someone could give their opinion on my current set-up before it blows up

Here goes, 08 DRZ 400 SM 100% street ,300-700 ft. elev.

used CPW slant body 39 mm FCR with sudco air boot and zip tie on a.p. linkage,

MRD/SSW uncorked 👍,

3x3 mod , twin air filter,

300-700 ft. elev.

160 main, 200 maj, EMN clip 3 , 45 pilot,

1 turn out air jet, t handle fuel screw does nothing , I ordered an new one from TT

CR8 EK spark plug looks grey / off white with 5 hrs. on it.

New MRD pipe has turned blue past the bend and discoloured all the way to the connection ( near heat sheild ). The bike pulls hard through all gears , stumbles a little from a stop , constant decel popping , W/O then chop will cause it to backfire multiple times

My concearn is too lean? , and why dosen't my fuel screw work?

don't want to burn out motor, should I use a wide band a.f.r, what brand and model for best value?

Edited by arcteryxbird
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  • 5 months later...

You are definitely lean. I have an SM that I swapped an E motor, FCR, and CDI to.. I have MRD/SSW open with a K/N filter, 3/3 mod. I dont run lean and my pipe doesnt get that hot. I am about to pull the carb and rejet it today.. (hence me searching the threads. If i get it running right i will let you know what i did.

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  • 4 weeks later...

Another thing to look at.. your fuel screw should be 2 turns out on the FCR39H. Eddie mod on the AP will stop low end bog.. Backfire on decel usually is issue with leak in exhaust.. i get the same thing with my SSW.. haven't messed with it to figure out where it is leaking though.. but its not necessarily bad or good. If you think about it.. just a tiny leak can cause it to backfire.. and the SSW doesnt have a clamp where it joins the header. I will be messing around with it in a little bit..

still.. it shouldnt be running that lean.. your pipe shouldnt be discoloring.. why did you change your MAJ?

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Too,lean? No, your jetting is close and a lot of your problem is mis-information.

First, set the adjustable slow air jet in the left side of the carb bell to 7/8ths of a turn from gently closed.

Unlesss the tip of your fuel screw is missing, you do not njeed a new one. I hope you did not order an alloy one, they are often junk.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

You cannot read a plug with todays fuels. You could 40 years ago.

To deal with the stumble from a stop, turn the AP tioming scew 1/2 turn CCW.

Pipe discoloration is normal. Let the bike sit and idle at night and it will glow, also normal.

Decel popping is normal, You have nearly no muffler to absord the normal pops, so now you hear them.

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Thanks guys, I will change my screw back a touch to 7/8 ths ( currently at 1 ) I did get the new steel fuel screw , but still no change. The carb was purchsed used , originally from CPW so it does not have the AP adjustment, but it is zip tied , also the diaphram rivet is flush as per mod. I have also double checked my valve timming and lash , spot on.

I can live with the popping ( actually like it ) just wanted to be sure it is the pipe and not the jetting.

As far as the fuel screw I guess I will just leave it at 2 turns out and ride it!

Thanks again for your advice

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The slow air jet being opened so far pu the pilot jet out out of the range of the fuel screw adjustment and therefore tany turns did not thing. Basically, it is like a bucket of water and the ocean, the bucket does little. But insted of the ocean, you had a kitchen sink, then the bucket would have an effect. Once you set the Adjustabe slow air jet, the fuel screw will work properly.

Yes, on your card, you ben the 'forks' a tiny bit. Search for the "Eddie Mod".

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